1. Field of the Invention
The present invention relates to an apparatus for growing thin films on a surface of a substrate. More particularly, the present invention relates to an apparatus for producing thin films on a surface of a substrate by subjecting the substrate to alternately repeated surface reactions of vapor-phase reactants.
2. Description of the Related Art
In manufacturing semiconductor devices, various apparatuses and processes have been developed to provide a high quality thin film on a substrate. Several methods have been used to form a thin film, employing surface reaction of a semiconductor substrate. The methods include vacuum evaporation deposition, Molecular Beam Epitaxy (MBE), different variants of Chemical Vapor Deposition (CVD) (including low-pressure and organometallic CVD and plasma-enhanced CVD), and Atomic Layer Epitaxy (ALE). ALE was studied extensively for semiconductor deposition and electroluminescent display applications, and has been more recently referred to as Atomic Layer Deposition (ALD) for the deposition of a variety of materials.
ALD is a method of depositing thin films on a surface of a substrate through a sequential introduction of various precursor species to the substrate. The growth mechanism tends to rely on the adsorption of a first precursor on the active sites of the substrate. Conditions are such that no more than a monolayer forms, thereby self-terminating the process. Exposing the substrate to the first precursor is usually followed by a purging stage or other removal process (e.g., a “pump down”) wherein any excess amounts of the first precursor as well as any reaction by-products are removed from the reaction chamber. The second precursor is then introduced into the reaction chamber at which time it reacts with the first precursor and this reaction creates the desired thin film. The reaction terminates once all of the available first precursor species adsorbed on the substrate has been reacted. A second purge or other removal stage is then performed which rids the reaction chamber of any remaining second precursor or possible reaction by-products. This cycle can be repeated to grow the film to a desired thickness. The cycles can also be more complex. For example, the cycles may include three or more reactant pulses separated by purge or other removal steps and in some variants pulses can include more than one reactant simultaneously.
In typical ALD processes, reactants are pulsed into a reaction space while the temperature of the reaction space is maintained within a certain range. The temperature range may be in an ALD window above the condensation temperatures of the reactants and below the thermal decomposition temperatures of the reactants. A thin film is formed by saturative surface reactions. Typically, a thin film having a uniform thickness may be formed on the surface of a substrate, regardless of the surface roughness of the substrate. A thin film formed by an ALD process has relatively less impurities, and has relatively high quality. One of the recognized advantages of ALD over other deposition processes is that it is self-saturating and uniform as long as the temperature is within the ALD window and sufficient reactant is provided to saturate the surface in each pulse. Thus, neither temperature nor gas supply needs to be perfectly uniform in order to get uniform deposition.
Lateral or horizontal flow ALD reactors have been proposed. In a lateral flow ALD reactor, gases flow laterally or horizontally over and parallel to the top surface of a substrate. In such a lateral flow ALD reactor, flows of the gases are relatively fast and simple. Thus, high speed switching of gas supplies can be achieved, thereby reducing time for sequentially supplying process gases, and thus increasing throughput. Such increased speed is important because ALD process is inherently slow by comparison to PVD or CVD due to the need for numerous gas switching operations and growth rates typically under one monolayer per cycle. Examples of lateral flow ALD reactors are disclosed in U.S. Pat. No. 5,711,811; U.S. Pat. No. 6,539,891; U.S. Pat. No. 6,562,140; and U.S. Patent Application Publication No. 2006-0249077. In these examples, the ALD reactors have a reaction chamber with a substantially constant gap between the top surface of a substrate processed therein and a reactor surface facing the top surface of the substrate, such that a gas flow over the substrate is a substantially uniform laminar flow. Such reaction chambers may be referred to as “cross-flow reaction chambers.”
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form prior art already known in this country to a person of ordinary skill in the art.